The invention concerns a mobile radio with a time synchronization apparatus and a method for performing time synchronization between a base station and the mobile radio.
In cellular communication, mobile radios (i.e.-xe2x80x9cradioxe2x80x9d) and radio base stations (i.e.-xe2x80x9cbasexe2x80x9d) exchange data and control signals. The base can serve more than one radio, and several bases can serve a plurality of radios in a defined geographic area. A single radio generally communicates with one base at a time. The radio and base should be time synchronized in order for the transmitted and received signals to be properly interpreted by the radio and the base.
In both radio and base there are timing units for timing events executed within the radio and the base. Such timing units can include one or more counters. The counters are used to time various events occurring within the radio and base and for measuring time intervals. For example, one counter can count the number of communication frames being exchanged between base and radio, and another counter can be used to trigger events that occur within a communication frame. In order for the radio and base to function properly, the timing counters in the radio and the base should be periodically synchronized.
Offset between the timing counters of the radio and base can occur, for example, as a result of a handover of a radio between two base stations or from movement of the radio which changes the propagation time of the signals exchanged between the base and radio. In order to synchronize the timing counter of the mobile radio and the timing counter of base station, timing signals are periodically sent by one to the other and an offset is calculated and one or both timing counters adjusted. Usually the timing counter in the mobile radio is adjusted.
Prior art arrangements for synchronizing a mobile radio timing counter have several disadvantages. Resetting the timing counter can interfere with normal operation of the radio, especially when the timing reset occurs while the timing unit is in the middle of scheduling or triggering some operation within the radio.
Another problem of the prior art is that there is often a lack of synchronization between a microprocessor controlling the radio and the timing unit. If the microprocessor initiates a timer update procedure just as the timing counter is rolling over to begin a new count, an entire count period can be missed.
A further problem in the prior art is the need to compensate for the time lapse between reading the timing counter value and writing an updated value to the timing counter. This time lapse can vary, e.g., due to microprocessor interrupts, thereby causing the synchronization to be inaccurate.
Accordingly, there is an ongoing need for an improved apparatus and method for synchronizing timing in separated radios.